Gene-centered view of evolution
Encyclopedia
The gene-centered view of evolution, gene selection theory or selfish gene theory holds that evolution
occurs through the differential survival of competing gene
s, increasing the frequency of those allele
s whose phenotypic
effects successfully promote their own propagation, with gene defined as "not just one single physical bit of DNA [but] all replicas of a particular bit of DNA distributed throughout the world". The proponents of this viewpoint argue that, since heritable information is passed from generation to generation almost exclusively by genetic material
, natural selection
and evolution are best considered from the perspective of genes.
This is in contrast to the organism-centered viewpoint adopted historically by biologists. Proponents of the gene-centered viewpoint argue that it permits understanding of diverse phenomena such as altruism
and intragenomic conflict
that are otherwise difficult to explain from an organism-focused perspective.
The gene-centered view of evolution is a synthesis of the theory of evolution
by natural selection
, the particulate inheritance theory
and the non-transmission of acquired characters. It states that those genes whose phenotypic effects successfully promote their own propagation will be favorably selected in detriment to their competitors. This process produces adaptations for the benefit of genes
that promote the reproductive success of the organism
, or of other organisms containing the same gene (kin altruism and green-beard effects), or even only its own propagation in detriment to the other genes of the genome (intragenomic conflict).
is a different way of looking at the basis of evolutionary development. It turns the whole solution of evolution inside-out for the purpose of examination. What this new perspective reveals is a more easily understood model for the evolution of social characteristics such as selfishness and altruism that much of the study of evolution, caught up in the survival of the individual organisms, overlooks.
made it clear that the inheritance of acquired characters was not an evolutionary factor
in a physical sense and identified genes as lasting entities that survive through many generations. Maynard Smith summarized the issue:
The rejection of the inheritance of acquired characters, combined with the classical mathematical evolutionary biology developed by Ronald Fisher
, J. B. S. Haldane
and Sewall Wright
, paved the way to the formulation of the selfish-gene theory. For cases where environment can influence heredity, see epigenetics
.
was developed mainly in the works W. D. Hamilton
, Colin Pittendrigh
and George C. Williams
. It was later popularized by Richard Dawkins
in his books The Selfish Gene
(1976) and The Extended Phenotype
(1982).
According to Williams' 1966 book Adaptation and Natural Selection
,
Williams argued that "[t]he natural selection of phenotype
s cannot in itself produce cumulative change, because phenotypes are extremely temporary manifestations". Each phenotype is the unique product of the interaction between genome and environment. It does not matter how fit and fertile a phenotype is, it will eventually be destroyed and will never be duplicated.
Since 1954, it has been known that DNA
is the main physical substrate to genetic information, and it is capable of high-fidelity replication
through many generations. So, a particular sequence of DNA can have a high permanence and a low rate of endogenous change.
In normal sexual reproduction, an entire genome
is the unique combination of father's and mother's chromosomes produced at the moment of fertilization. It is generally destroyed with its organism, because "meiosis
and recombination
destroy genotypes as surely as death". Only half of it is transmitted to each descendant due to independent segregation.
The gene as an informational entity persists for an evolutionarily significant span of time through a lineage of many physical copies.
In his book River out of Eden
, Dawkins coins the phrase God's utility function
to explain his view on genes as units of selection. He uses this phrase as a synonym of the "meaning of life
" or the "purpose of life". By rephrasing the word purpose in terms of what economists call a utility function, meaning "that which is maximized", Dawkins attempts to reverse-engineer
the purpose in the mind of the Divine Engineer of Nature, or the Utility Function of God. Finally, Dawkins argues that it is a mistake to assume that an ecosystem
or a species
as a whole exists for a purpose. He writes that it is incorrect to suppose that individual organisms lead a meaningful life either; in nature, only genes have a utility function – to perpetuate their own existence with indifference to great sufferings inflicted upon the organisms they build, exploit and discard.
The phenotypic effect of a particular gene is contingent on its environment, including the fellow genes constituting with it the total genome. A gene never has a fixed effect, so how is it possible to speak of a gene for long legs? It is because of the phenotypic differences between alleles. One may say that one allele, all other things being equal or varying within certain limits, causes greater legs than its alternative. This difference enables the scrutiny of natural selection.
"A gene can have multiple phenotypic effects, each of which may be of positive, negative or neutral value. It is the net selective value of a gene's phenotypic effect that determines the fate of the gene". For instance, a gene can cause its bearer to have greater reproductive success at a young age, but also cause a greater likelihood of death at a later age. If the benefit outweighs the harm, averaged out over the individuals and environments in which the gene happens to occur, then phenotypes containing the gene will generally be positively selected and thus the abundance of that gene in the population will increase.
Even so, it becomes necessary to model the genes in combination with their vehicle as well as in combination with the vehicle’s environment.
The result is that "the prevalent genes in a sexual population must be those that, as a mean condition, through a large number of genotypes in a large number of situations, have had the most favourable phenotypic effects for their own replication". In other words, we expect selfish genes ("selfish" meaning that it promotes its own survival without necessarily promoting the survival of the organism, group or even species). This theory implies that adaptation
s are the phenotypic effects of genes to maximize their representation in future generations. An adaptation is maintained by selection if it promotes genetic survival directly, or else some subordinate goal that ultimately contributes to successful reproduction.
A gene in a somatic
cell of an individual may forego replication to promote the transmission of its copies in the germ line cells. It ensures the high value of p = 1 due to their constant contact and their common origin from the zygote
.
The kin selection
theory predicts that a gene may promote the recognition of kinship by historical continuity: a mammalian mother learns to identify her own offspring in the act of giving birth; a male preferentially directs resources to the offspring of mothers with whom he has copulated; the other chicks in a nest are siblings; and so on. The expected altruism between kin is calibrated by the value of p, also known as the coefficient of relatedness
. For instance, an individual has a p = 1/2 in relation to his brother, and p = 1/8 to his cousin, so we would expect, ceteris paribus
, greater altruism among brothers than among cousins. In this vein, geneticist J.B.S. Haldane famously joked, "Would I lay down my life to save my brother? No, but I would to save two brothers or eight cousins". However, examining the human propensity for altruism, kin selection theory seems incapable of explaining cross-familiar, cross-racial and even cross-species acts of kindness.
s gained their name from a thought-experiment of Richard Dawkins
, who considered the possibility of a gene that caused its possessors to develop a green beard and to be nice to other green-bearded individuals. Since then, 'green-beard effect' has come to refer to forms of genetic self-recognition in which a gene in one individual might direct benefits to other individuals that possess the gene. Such genes are essentially especially selfish, benefiting themselves regardless of the fates of their vehicles.
On the other hand, a single trait, group reciprocal kindness, is capable of explaining the vast majority of altruism that is generally accepted as “good” by modern societies. Imagine a green-bearding behavioral trait whose recognition does not depend on the recognition of some external feature such as beard color, but relies on recognition of the behavior itself. Imagine now that the behavior is altruistic. The success of such a trait in sufficiently intelligent and undeceived organisms is implicit. Moreover, the existence of such a trait predicts a tendency for kindness to unrelated organisms that are apparently kind, even if the organisms are of a completely different species. Moreover, the gene need not be exactly the same, so long as the effect is similar. Multiple versions of the gene—or even meme
—would have virtually the same effect in a sort of symbiotic green-bearding cycle of altruism.
and arises when one gene promotes its own replication in detriment to other genes in the genome. The classic example is segregation distorter genes that cheat during meiosis
or gametogenesis
and end up in more than half of the functional gamete
s. These genes persist even resulting in reduced fertility
. Egbert Leigh compared the genome to "a parliament of genes: each acts in its own self-interest, but if its acts hurt the others, they will combine together to suppress it" to explain the relative low occurrence of intragenomic conflict.
, paleontologist Stephen Jay Gould
, biologist and anthropologist David Sloan Wilson
and philosopher Elliott Sober
.
Writing in the New York Review of Books, Gould has characterized the gene-centered perspective as confusing book-keeping with causality
. Gould views selection as working on many levels, and has called attention to a hierarchical perspective of selection. Gould also called the claims of Selfish Gene "strict adaptationism
", "ultra-Darwinism", and "Darwinian fundamentalism
", describing them as excessively "reductionist". He saw the theory as leading to a simplistic "algorithmic" theory of evolution, or even to the re-introduction of a teleological principle
. Mayr went so far as to say "Dawkins' basic theory of the gene being the object of evolution is totally non-Darwinian".
Gould also addressed the issue of selfish genes in his essay 'Caring groups and selfish genes'. Gould acknowledged that Dawkins was not imputing conscious action to genes, but simply using a shorthand metaphor commonly found in evolutionary writings. To Gould, the fatal flaw was that "no matter how much power Dawkins wishes to assign to genes, there is one thing that he cannot give them – direct visibility to natural selection". Rather, the unit of selection is the phenotype, not the genotype, because it is phenotypes which interact with the environment at the natural-selection interface. So, in Kim Sterelny
's summation of Gould's view, "gene differences do not cause evolutionary changes in populations, they register those changes". Richard Dawkins replied to this criticism in a later book, The Extended Phenotype, that Gould confused particulate genetics with particulate embryology, stating that genes do "blend", as far as their effects on developing phenotypes are concerned, but that they do not blend as they replicate and recombine down the generations.
Since Gould's death in 2002, Niles Eldredge
has continued with counter-arguments to gene-centered natural selection. Eldredge notes that in Dawkins' book A Devil's Chaplain
, which was published just before Eldredge's book, "Richard Dawkins comments on what he sees as the main difference between his position and that of the late Stephen Jay Gould. He concludes that it is his own vision that genes play a causal role in evolution", while Gould (and Eldredge) "sees genes as passive recorders of what worked better than what".
equation which is a mathematical description of evolution
and natural selection
. The Price equation was derived by George R. Price
, working in London to rederive W.D. Hamilton's work on kin selection
.
and George C. Williams
, other biologist
s and philosophers have expanded and refined the selfish-gene theory, such as John Maynard Smith
, George R. Price
, Robert Trivers
, David Haig
, Helena Cronin
, David Hull
, Philip Kitcher and Daniel C. Dennett.
Individuals opposing this gene-centric view include Ernst Mayr
, Stephen Jay Gould
, David Sloan Wilson
and philosopher Elliott Sober
.
Proponents of multilevel selection (MLS) include E.O. Wilson, David Sloan Wilson
, Elliott Sober
, Richard E. Michod and Samir Okasha.
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
occurs through the differential survival of competing gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s, increasing the frequency of those allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s whose phenotypic
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
effects successfully promote their own propagation, with gene defined as "not just one single physical bit of DNA [but] all replicas of a particular bit of DNA distributed throughout the world". The proponents of this viewpoint argue that, since heritable information is passed from generation to generation almost exclusively by genetic material
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
, natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
and evolution are best considered from the perspective of genes.
This is in contrast to the organism-centered viewpoint adopted historically by biologists. Proponents of the gene-centered viewpoint argue that it permits understanding of diverse phenomena such as altruism
Altruism in animals
Altruism is a well-documented animal behaviour, which appears most obviously in kin relationships but may also be evident amongst wider social groups, in which an animal sacrifices its own well-being for the benefit of another animal.- Overview :...
and intragenomic conflict
Intragenomic conflict
The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication...
that are otherwise difficult to explain from an organism-focused perspective.
The gene-centered view of evolution is a synthesis of the theory of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
by natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
, the particulate inheritance theory
Particulate inheritance theory
Particulate inheritance is a pattern of inheritance discovered by Mendelian theorists showing that characteristics can be passed from generation to generation through "discrete particles"...
and the non-transmission of acquired characters. It states that those genes whose phenotypic effects successfully promote their own propagation will be favorably selected in detriment to their competitors. This process produces adaptations for the benefit of genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
that promote the reproductive success of the organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
, or of other organisms containing the same gene (kin altruism and green-beard effects), or even only its own propagation in detriment to the other genes of the genome (intragenomic conflict).
Introduction
The gene-centered view of evolutionEvolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
is a different way of looking at the basis of evolutionary development. It turns the whole solution of evolution inside-out for the purpose of examination. What this new perspective reveals is a more easily understood model for the evolution of social characteristics such as selfishness and altruism that much of the study of evolution, caught up in the survival of the individual organisms, overlooks.
Acquired characteristics are not inherited
Discoveries in science such as the formulation of the central dogma of molecular biologyCentral dogma of molecular biology
The central dogma of molecular biology was first articulated by Francis Crick in 1958 and re-stated in a Nature paper published in 1970:In other words, the process of producing proteins is irreversible: a protein cannot be used to create DNA....
made it clear that the inheritance of acquired characters was not an evolutionary factor
Evolutionary factor
Evolutionary factors in biology are all factors that modify the gene pool in the evolutionary process.The most concise definition comes from population genetics:...
in a physical sense and identified genes as lasting entities that survive through many generations. Maynard Smith summarized the issue:
The rejection of the inheritance of acquired characters, combined with the classical mathematical evolutionary biology developed by Ronald Fisher
Ronald Fisher
Sir Ronald Aylmer Fisher FRS was an English statistician, evolutionary biologist, eugenicist and geneticist. Among other things, Fisher is well known for his contributions to statistics by creating Fisher's exact test and Fisher's equation...
, J. B. S. Haldane
J. B. S. Haldane
John Burdon Sanderson Haldane FRS , known as Jack , was a British-born geneticist and evolutionary biologist. A staunch Marxist, he was critical of Britain's role in the Suez Crisis, and chose to leave Oxford and moved to India and became an Indian citizen...
and Sewall Wright
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
, paved the way to the formulation of the selfish-gene theory. For cases where environment can influence heredity, see epigenetics
Epigenetics
In biology, and specifically genetics, epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence – hence the name epi- -genetics...
.
The gene as the unit of selection
The view of the gene as the unit of selectionUnit of selection
A unit of selection is a biological entity within the hierarchy of biological organisation that is subject to natural selection...
was developed mainly in the works W. D. Hamilton
W. D. Hamilton
William Donald Hamilton FRS was a British evolutionary biologist, widely recognised as one of the greatest evolutionary theorists of the 20th century....
, Colin Pittendrigh
Colin Pittendrigh
Colin Pittendrigh was a US-American biologist of English parentage. He is a co-founder of modern chronobiology along with Jürgen Aschoff and Erwin Bünning.-Life:...
and George C. Williams
George C. Williams
Professor George Christopher Williams was an American evolutionary biologist.Williams was a professor emeritus of biology at the State University of New York at Stony Brook. He was best known for his vigorous critique of group selection. The work of Williams in this area, along with W. D...
. It was later popularized by Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
in his books The Selfish Gene
The Selfish Gene
The Selfish Gene is a book on evolution by Richard Dawkins, published in 1976. It builds upon the principal theory of George C. Williams's first book Adaptation and Natural Selection. Dawkins coined the term "selfish gene" as a way of expressing the gene-centred view of evolution as opposed to the...
(1976) and The Extended Phenotype
The Extended Phenotype
The Extended Phenotype is a biological concept introduced by Richard Dawkins in a 1982 book with the same title. The main idea is that phenotype should not be limited to biological processes such as protein biosynthesis or tissue growth, but extended to include all effects that a gene has on its...
(1982).
According to Williams' 1966 book Adaptation and Natural Selection
Adaptation and Natural Selection
Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought is a 1966 book by the American evolutionary biologist George C. Williams...
,
Williams argued that "[t]he natural selection of phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
s cannot in itself produce cumulative change, because phenotypes are extremely temporary manifestations". Each phenotype is the unique product of the interaction between genome and environment. It does not matter how fit and fertile a phenotype is, it will eventually be destroyed and will never be duplicated.
Since 1954, it has been known that DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
is the main physical substrate to genetic information, and it is capable of high-fidelity replication
DNA replication
DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...
through many generations. So, a particular sequence of DNA can have a high permanence and a low rate of endogenous change.
In normal sexual reproduction, an entire genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
is the unique combination of father's and mother's chromosomes produced at the moment of fertilization. It is generally destroyed with its organism, because "meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
and recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
destroy genotypes as surely as death". Only half of it is transmitted to each descendant due to independent segregation.
The gene as an informational entity persists for an evolutionarily significant span of time through a lineage of many physical copies.
In his book River out of Eden
River out of Eden
River Out of Eden: A Darwinian View of Life is a 1995 popular science book by Richard Dawkins. The book is about Darwinian evolution and includes summaries of the topics covered in his earlier books, The Selfish Gene, The Extended Phenotype and The Blind Watchmaker. It is part of the Science...
, Dawkins coins the phrase God's utility function
God's utility function
God's utility function is a phrase coined by Richard Dawkins in his book River Out of Eden. "God's utility function" is the third chapter in this book. Dawkins uses this phrase to expound the Gene-centered view of evolution by equating the phrase to the meaning of life or the purpose of life...
to explain his view on genes as units of selection. He uses this phrase as a synonym of the "meaning of life
Meaning of life
The meaning of life constitutes a philosophical question concerning the purpose and significance of life or existence in general. This concept can be expressed through a variety of related questions, such as "Why are we here?", "What is life all about?", and "What is the meaning of it all?" It has...
" or the "purpose of life". By rephrasing the word purpose in terms of what economists call a utility function, meaning "that which is maximized", Dawkins attempts to reverse-engineer
Reverse engineering
Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...
the purpose in the mind of the Divine Engineer of Nature, or the Utility Function of God. Finally, Dawkins argues that it is a mistake to assume that an ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
or a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
as a whole exists for a purpose. He writes that it is incorrect to suppose that individual organisms lead a meaningful life either; in nature, only genes have a utility function – to perpetuate their own existence with indifference to great sufferings inflicted upon the organisms they build, exploit and discard.
Organisms as vehicles
Genes are not naked in the world. They are usually packed together inside a genome, which is itself contained inside an organism. Genes group together into genomes because "genetic replication makes use of energy and substrates that are supplied by the metabolic economy in much greater quantities than would be possible without a genetic division of labour". They build vehicles to promote their mutual interests of jumping into the next generation of vehicles. As Dawkins puts it, organisms are the "survival machines" of genes.The phenotypic effect of a particular gene is contingent on its environment, including the fellow genes constituting with it the total genome. A gene never has a fixed effect, so how is it possible to speak of a gene for long legs? It is because of the phenotypic differences between alleles. One may say that one allele, all other things being equal or varying within certain limits, causes greater legs than its alternative. This difference enables the scrutiny of natural selection.
"A gene can have multiple phenotypic effects, each of which may be of positive, negative or neutral value. It is the net selective value of a gene's phenotypic effect that determines the fate of the gene". For instance, a gene can cause its bearer to have greater reproductive success at a young age, but also cause a greater likelihood of death at a later age. If the benefit outweighs the harm, averaged out over the individuals and environments in which the gene happens to occur, then phenotypes containing the gene will generally be positively selected and thus the abundance of that gene in the population will increase.
Even so, it becomes necessary to model the genes in combination with their vehicle as well as in combination with the vehicle’s environment.
Selfish-gene theory
The selfish-gene theory of natural selection can be restated as follows:The result is that "the prevalent genes in a sexual population must be those that, as a mean condition, through a large number of genotypes in a large number of situations, have had the most favourable phenotypic effects for their own replication". In other words, we expect selfish genes ("selfish" meaning that it promotes its own survival without necessarily promoting the survival of the organism, group or even species). This theory implies that adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
s are the phenotypic effects of genes to maximize their representation in future generations. An adaptation is maintained by selection if it promotes genetic survival directly, or else some subordinate goal that ultimately contributes to successful reproduction.
Individual altruism, genetic egoism
The gene is a unit of hereditary information that exists in many physical copies in the world, and which particular physical copy will be replicated and originate new copies does not matter from the gene's point of view. A selfish gene could be favored by selection by producing altruism among organisms containing it. The idea is summarized as follows:A gene in a somatic
Somatic
The term somatic means 'of the body',, relating to the body. In medicine, somatic illness is bodily, not mental, illness. The term is often used in biology to refer to the cells of the body in contrast to the germ line cells which usually give rise to the gametes...
cell of an individual may forego replication to promote the transmission of its copies in the germ line cells. It ensures the high value of p = 1 due to their constant contact and their common origin from the zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
.
The kin selection
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...
theory predicts that a gene may promote the recognition of kinship by historical continuity: a mammalian mother learns to identify her own offspring in the act of giving birth; a male preferentially directs resources to the offspring of mothers with whom he has copulated; the other chicks in a nest are siblings; and so on. The expected altruism between kin is calibrated by the value of p, also known as the coefficient of relatedness
Coefficient of relationship
In population genetics, Sewall Wright's coefficient of relationship or coefficient of relatedness or relatedness or r is defined as 2 times the Coefficient of Inbreeding...
. For instance, an individual has a p = 1/2 in relation to his brother, and p = 1/8 to his cousin, so we would expect, ceteris paribus
Ceteris paribus
or is a Latin phrase, literally translated as "with other things the same," or "all other things being equal or held constant." It is an example of an ablative absolute and is commonly rendered in English as "all other things being equal." A prediction, or a statement about causal or logical...
, greater altruism among brothers than among cousins. In this vein, geneticist J.B.S. Haldane famously joked, "Would I lay down my life to save my brother? No, but I would to save two brothers or eight cousins". However, examining the human propensity for altruism, kin selection theory seems incapable of explaining cross-familiar, cross-racial and even cross-species acts of kindness.
Green-beard effect
Green-beard effectGreen-beard effect
The gene-centered view of evolution postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication...
s gained their name from a thought-experiment of Richard Dawkins
Richard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
, who considered the possibility of a gene that caused its possessors to develop a green beard and to be nice to other green-bearded individuals. Since then, 'green-beard effect' has come to refer to forms of genetic self-recognition in which a gene in one individual might direct benefits to other individuals that possess the gene. Such genes are essentially especially selfish, benefiting themselves regardless of the fates of their vehicles.
Kindness
On the other hand, a single trait, group reciprocal kindness, is capable of explaining the vast majority of altruism that is generally accepted as “good” by modern societies. Imagine a green-bearding behavioral trait whose recognition does not depend on the recognition of some external feature such as beard color, but relies on recognition of the behavior itself. Imagine now that the behavior is altruistic. The success of such a trait in sufficiently intelligent and undeceived organisms is implicit. Moreover, the existence of such a trait predicts a tendency for kindness to unrelated organisms that are apparently kind, even if the organisms are of a completely different species. Moreover, the gene need not be exactly the same, so long as the effect is similar. Multiple versions of the gene—or even meme
Meme
A meme is "an idea, behaviour or style that spreads from person to person within a culture."A meme acts as a unit for carrying cultural ideas, symbols or practices, which can be transmitted from one mind to another through writing, speech, gestures, rituals or other imitable phenomena...
—would have virtually the same effect in a sort of symbiotic green-bearding cycle of altruism.
Deceit
Whenever recognition plays a role in evolution, so does deception. Just like the harmless lizard that has evolved a pattern that mimics its poisonous cousin and therefore tricks predators, the selfish creature may pretend to be kind by “growing a green beard” (whatever that green beard may be). Thus green-bearding and the selfish-gene theory also give rise to an explanation for the evolution of lies and deceit, characteristics that do not benefit the population as a whole.Intragenomic conflict
As genes are capable of producing individual altruism, they are capable of producing conflict among genes inside the genome of one individual. This phenomenon was called intragenomic conflictIntragenomic conflict
The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication...
and arises when one gene promotes its own replication in detriment to other genes in the genome. The classic example is segregation distorter genes that cheat during meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
or gametogenesis
Gametogenesis
Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes,...
and end up in more than half of the functional gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s. These genes persist even resulting in reduced fertility
Fertility
Fertility is the natural capability of producing offsprings. As a measure, "fertility rate" is the number of children born per couple, person or population. Fertility differs from fecundity, which is defined as the potential for reproduction...
. Egbert Leigh compared the genome to "a parliament of genes: each acts in its own self-interest, but if its acts hurt the others, they will combine together to suppress it" to explain the relative low occurrence of intragenomic conflict.
Criticism
Prominent opponents of this gene-centric view of evolution include evolutionary biologist Ernst MayrErnst Mayr
Ernst Walter Mayr was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist...
, paleontologist Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
, biologist and anthropologist David Sloan Wilson
David Sloan Wilson
David Sloan Wilson is an American evolutionary biologist and a Distinguished Professor of Biological Sciences and Anthropology at Binghamton University. He is a son of the author Sloan Wilson.-Academic career:...
and philosopher Elliott Sober
Elliott Sober
Elliott Sober is Hans Reichenbach Professor and William F. Vilas Research Professor in the Department of Philosophy at University of Wisconsin–Madison. Sober is noted for his work in philosophy of biology and general philosophy of science. Sober taught for one year at Stanford University and has...
.
Writing in the New York Review of Books, Gould has characterized the gene-centered perspective as confusing book-keeping with causality
Causality
Causality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....
. Gould views selection as working on many levels, and has called attention to a hierarchical perspective of selection. Gould also called the claims of Selfish Gene "strict adaptationism
Adaptationism
Adaptationism is a set of methods in the evolutionary sciences for distinguishing the products of adaptation from traits that arise through other processes. It is employed in fields such as ethology and evolutionary psychology that are concerned with identifying adaptations...
", "ultra-Darwinism", and "Darwinian fundamentalism
Fundamentalism
Fundamentalism is strict adherence to specific theological doctrines usually understood as a reaction against Modernist theology. The term "fundamentalism" was originally coined by its supporters to describe a specific package of theological beliefs that developed into a movement within the...
", describing them as excessively "reductionist". He saw the theory as leading to a simplistic "algorithmic" theory of evolution, or even to the re-introduction of a teleological principle
Teleology
A teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...
. Mayr went so far as to say "Dawkins' basic theory of the gene being the object of evolution is totally non-Darwinian".
Gould also addressed the issue of selfish genes in his essay 'Caring groups and selfish genes'. Gould acknowledged that Dawkins was not imputing conscious action to genes, but simply using a shorthand metaphor commonly found in evolutionary writings. To Gould, the fatal flaw was that "no matter how much power Dawkins wishes to assign to genes, there is one thing that he cannot give them – direct visibility to natural selection". Rather, the unit of selection is the phenotype, not the genotype, because it is phenotypes which interact with the environment at the natural-selection interface. So, in Kim Sterelny
Kim Sterelny
Kim Sterelny is an Australian philosopher and professor of philosophy in the Research School of Social Sciences at Australian National University and Victoria University of Wellington. He is the winner of several international prizes in the philosophy of science, and editor of Biology and Philosophy...
's summation of Gould's view, "gene differences do not cause evolutionary changes in populations, they register those changes". Richard Dawkins replied to this criticism in a later book, The Extended Phenotype, that Gould confused particulate genetics with particulate embryology, stating that genes do "blend", as far as their effects on developing phenotypes are concerned, but that they do not blend as they replicate and recombine down the generations.
Since Gould's death in 2002, Niles Eldredge
Niles Eldredge
Niles Eldredge is an American paleontologist, who, along with Stephen Jay Gould, proposed the theory of punctuated equilibrium in 1972.-Education:...
has continued with counter-arguments to gene-centered natural selection. Eldredge notes that in Dawkins' book A Devil's Chaplain
A Devil's Chaplain
A Devil's Chaplain, subtitled Reflections on Hope, Lies, Science, and Love is a 2003 book of selected essays and other writings by Richard Dawkins. Published five years after his previous book Unweaving the Rainbow, it contains 32 essays covering subjects including pseudoscience, genetic...
, which was published just before Eldredge's book, "Richard Dawkins comments on what he sees as the main difference between his position and that of the late Stephen Jay Gould. He concludes that it is his own vision that genes play a causal role in evolution", while Gould (and Eldredge) "sees genes as passive recorders of what worked better than what".
Price equation
The Price equation (also known as Price's equation) is a covarianceCovariance
In probability theory and statistics, covariance is a measure of how much two variables change together. Variance is a special case of the covariance when the two variables are identical.- Definition :...
equation which is a mathematical description of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
and natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
. The Price equation was derived by George R. Price
George R. Price
George Robert Price was an American population geneticist. Originally a physical chemist and later a science journalist, he moved to London in 1967, where he worked in theoretical biology at the Galton Laboratory, making three important contributions: first, rederiving W.D...
, working in London to rederive W.D. Hamilton's work on kin selection
Kin selection
Kin selection refers to apparent strategies in evolution that favor the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Charles Darwin was the first to discuss the concept of group/kin selection...
.
Main figures in selection debate
Besides Richard DawkinsRichard Dawkins
Clinton Richard Dawkins, FRS, FRSL , known as Richard Dawkins, is a British ethologist, evolutionary biologist and author...
and George C. Williams
George C. Williams
Professor George Christopher Williams was an American evolutionary biologist.Williams was a professor emeritus of biology at the State University of New York at Stony Brook. He was best known for his vigorous critique of group selection. The work of Williams in this area, along with W. D...
, other biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
s and philosophers have expanded and refined the selfish-gene theory, such as John Maynard Smith
John Maynard Smith
John Maynard Smith,His surname was Maynard Smith, not Smith, nor was it hyphenated. F.R.S. was a British theoretical evolutionary biologist and geneticist. Originally an aeronautical engineer during the Second World War, he took a second degree in genetics under the well-known biologist J.B.S....
, George R. Price
George R. Price
George Robert Price was an American population geneticist. Originally a physical chemist and later a science journalist, he moved to London in 1967, where he worked in theoretical biology at the Galton Laboratory, making three important contributions: first, rederiving W.D...
, Robert Trivers
Robert Trivers
Robert L. Trivers is an American evolutionary biologist and sociobiologist and Professor of Anthropology and Biological Sciences at Rutgers University. Trivers is most noted for proposing the theories of reciprocal altruism , parental investment , facultative sex ratio determination , and...
, David Haig
David Haig (biologist)
David Haig, is an Australian evolutionary biologist and geneticist, professor in Harvard Department of Organismic and Evolutionary Biology. He is interested in intragenomic conflict, genomic imprinting and parent-offspring conflict, and wrote the book Genomic Imprinting and Kinship...
, Helena Cronin
Helena Cronin
Dr. Helena Cronin is a noted Darwinian philosopher and rationalist. She is the co-director of the CPNSS and the Darwin Centre at the London School of Economics...
, David Hull
David Hull
David Lee Hull was a philosopher with a particular interest in the philosophy of biology. In addition to his academic prominence, he was well-known as a gay man who fought for the rights of other gay and lesbian philosophers....
, Philip Kitcher and Daniel C. Dennett.
Individuals opposing this gene-centric view include Ernst Mayr
Ernst Mayr
Ernst Walter Mayr was one of the 20th century's leading evolutionary biologists. He was also a renowned taxonomist, tropical explorer, ornithologist, historian of science, and naturalist...
, Stephen Jay Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
, David Sloan Wilson
David Sloan Wilson
David Sloan Wilson is an American evolutionary biologist and a Distinguished Professor of Biological Sciences and Anthropology at Binghamton University. He is a son of the author Sloan Wilson.-Academic career:...
and philosopher Elliott Sober
Elliott Sober
Elliott Sober is Hans Reichenbach Professor and William F. Vilas Research Professor in the Department of Philosophy at University of Wisconsin–Madison. Sober is noted for his work in philosophy of biology and general philosophy of science. Sober taught for one year at Stanford University and has...
.
Proponents of multilevel selection (MLS) include E.O. Wilson, David Sloan Wilson
David Sloan Wilson
David Sloan Wilson is an American evolutionary biologist and a Distinguished Professor of Biological Sciences and Anthropology at Binghamton University. He is a son of the author Sloan Wilson.-Academic career:...
, Elliott Sober
Elliott Sober
Elliott Sober is Hans Reichenbach Professor and William F. Vilas Research Professor in the Department of Philosophy at University of Wisconsin–Madison. Sober is noted for his work in philosophy of biology and general philosophy of science. Sober taught for one year at Stanford University and has...
, Richard E. Michod and Samir Okasha.
See also
- Evolutionary biology